In the field of ornamental lighting, a recently recognized application exists in the use of large scale image projecting fixtures. These involve a permanently located fixture directed toward a large planar surface such as a building side and including not only a lamp within the fixture to illuminate the surface but provision for mounting a photographic transparency and suitable focusing optical system for projecting the image of the transparency on the wall or surface which now becomes a changeable work of art.
The basic concept is deceptively simple. In carrying out the design of such projector system, however, one must first provide a weather-tight enclosure and one, which maintains the weather tight connection when it is illuminated or not and whether exposed to sub freezing or 100-degree Fahrenheit temperature. The fixture must maintain its focus despite such temperature changes and to be relatively immune to interference by vandals.
A further need is that the exchanging of lamps and the exchanging of photographic transparencies or other image source must be clone simply and rapidly without the intervention of a skilled projectionist. Often the maintenance of exterior lighting is delegated to groundskeepers and electricians who have many other duties and are not in a position to devote much time or attention to exchanging lamps or image media while having to maintain proper focus and direction of the fixture. Often the exchange of lamps or image media might be done during daylight hours when it would be difficult and possible to precisely check the focus and direction of the fixture. Such requirements are not present for most other exterior lighting.